Daughter and husband inherit 50/50 unless will stating different.
If house purchased within marriage period, husband already owns 50% so on wife's death his share 75%, daughters share 25%.
Grandson will inherit nothing without a will.
Whereas my solar copes perfectly with switching between grid/solar/battery.
Not that it chooses grid much.
If you have an ATS, your solar isn't standard, the inverter does the switching for standard installs.